Waste materials containing noble metals refer to waste components, waste residues and waste water, which contain gold, silver, platinum, palladium, rhodium, ruthenium, iridium and/or other noble metals. Because noble metals are rare and valuable but difficult to refine, there are economic and social benefits to recycle the waste materials containing such noble metals.
Waste printed circuit boards (PCBs) have an implicit value due to abundance of precious metals contained therein. Hence, the recovery of precious metals becomes necessary for an effective waste management or recycling process and the same has become an area of interest for the innovators and waste management/recycling industries.
The treatment techniques commonly used are mechanical crush, hydrometallurgy, pyrometallurgy or their combinations. Various methods are known in the art for recovering silver, gold and platinum group metals (PMG's) from separated metal containing concentrates and semi-products.
The two main approaches are either pyrometallurgy or hydrometallurgy. In the pyrometallurgy process, the precious metals-bearing scrap is melted to a high temperature where the metals are maintained and the connecting matrix, e.g. polymers, is burnt. Air emissions and fugitive gases are issues for all smelter processes and even more so for bath smelting and oxidation smelters.
In the hydrometallurgy process, the metals are freed from the matrix by immersing in an appropriate solution. However, many of the hydrometallurgical plants become constrained and continually deal with accumulations of bleed solutions. These bleed solutions are treated in wastewater treatment plants. Solids from bleed solutions must be hauled off site.